Wellheads are called upon for support of hangers, test plugs and other equipment during drilling and completion phases in a well. Typically the wellhead will have a support shoulder and a reduced bore so that lowering the hanger past a certain point will cause the hanger to become supported. In some designs, multiple shoulders with the same diameter are used to reduce the load applied to each one. A load ring having multiple bearing areas is used in conjunction with these multiple support shoulders to support the hanger off the wellhead.
Some of the problems with such designs are the difficulty in machining to close tolerance a combination of multiple shoulders and a load ring having a similar profile so that when the load is applied, it is divided equally between the multiple load shoulders. Another problem with designs that require reduction in bore size is that it is not possible to advance the hanger past the support point without latching into the support shoulder. In situation where the hanger must be advanced beyond the support shoulder and later raised up and only then supported, the reduced bore designs are not effective. The reduced bore designs are also costly because they require over-sizing the wellhead in order to have the requisite minimum bore diameter in it. Even in designs that use a single load surface in the wellhead, problems arise in design of a load ring that could expand to the required dimensions without distortion while still being strong enough to carry the applied load. In some designs the groove into which the expanding load ring was destined to enter did not provide adequate guidance to deal with bending or twisting that could occur as the diameter was increased. In other designs the load ring on the hanger was left unprotected during run in and left exposed to potential physical damage before it was urged into the supporting position. In other designs voids are added to the load ring that is intended to be sprung into a groove in the wellhead in a manner that can weaken the ability of the ring to resist bending and torsional forces that can occur during its release into the wellhead grove and subsequent loading applied from the hanger weight. Some designs only use sloping contact shoulders that maximize radial load components and promote distortion of the load ring as its diameter grows.
Some examples of prior designs that include one or more of the above stated shortcomings can be seen in U.S. Pat. Nos. 5,839,512; 4,295,665; 5,209,521; 5,984,008; 6,202,745 B1; 6,598,673 B1 and 3,420,308.
The present invention seeks to address these issues with a design that is simple to manufacture and repair and provides full bore access in the wellhead. It features an energizing taper and a limit shoulder that share the load. The receiving groove is shaped to anticipate the potential distortions in the ring as its diameter is increased and bring the ring back to shape. The receiving groove, at its depth is designed to encounter the ring to lend further guidance and support. The load can be shared between the energizing taper and the limit shoulder. The ring can also be made from a high strength low modulus material to enhance load carrying capability while permitting spanning of larger radial distances. Various designs are contemplated including C-rings and segmented rings where the segments are held to each other in a variety of ways. Those skilled in the art will more readily appreciate the various aspects of the invention from a description of the preferred embodiment and the claims, which appear below.